The Beginning of Infinity

Alchemists had dreamed for centuries of transmuting base metals, such as iron or lead, into gold. They never came close to understanding what it would take to achieve that, so they never did so. But scientists in the twentieth century did, and so do stars when they explode as supernovae. Base metals can be transmuted into gold by stars and by intelligent beings who understand the process that powers stars, but by nothing else in the universe. As for the Milky Way, you will be told that, despite its insubstantial appearance, it is the most massive object that we can see with the naked eye, a galaxy that includes stars by the hundreds of billions bound by their mutual gravitation across tens of thousands of light-years. We are seeing it from the inside because we are part of it. You will be told that, although our night sky appears serene and largely changeless, the universe is seething with violent activity. Even a typical star converts millions of tons of mass into energy every second, with each gram releasing as much energy as an atom bomb. You will be told that, within the range of our best telescopes, which can see more galaxies than there are stars in our galaxy, there are several supernova explosions per second, each briefly brighter than all the other stars in its galaxy put together. We do not know where life and intelligence exist, if at all, outside our solar system, so we do not know how many of those explosions are horrendous tragedies. But we do know that a supernova devastates all the planets that may be orbiting it, wiping out all life that may exist there, including any intelligent beings, unless they have technology far superior to ours. Its neutrino radiation alone would kill a human at a range of billions of kilometers, even if that entire distance were filled with lead shielding. Yet, we owe our existence to supernovae. They are the source, through transmutation, of most of the elements of which our bodies and our planet are composed. There are phenomena that outshine supernovae. In March 2008, an X-ray telescope in Earth orbit detected an explosion of a type known as a gamma-ray burst 7.5 billion light-years away. That is halfway across the known universe. It was probably a single star collapsing to form a black hole, an object whose gravity is so intense that not even light can escape from its interior. The explosion was intrinsically brighter than a million supernovae and would have been visible with the naked eye from Earth, though only faintly and for only a few seconds, so it is unlikely that anyone here saw it. Supernovae last longer, typically fading on a timescale of months, which allowed astronomers to see a few in our galaxy even before the invention of telescopes. Another class of cosmic monsters, the intensely luminous objects known as quasars, are in a different league. Too distant to be seen with the naked eye, they can outshine a supernova for millions of years at a time. They are powered by massive black holes at the centers of galaxies, into which entire stars are falling, up to several per day for a large quasar, shredded by tidal effects as they spiral in. Intense magnetic fields channel some of the gravitational energy back out in the form of jets of high-energy particles, which illuminate the surrounding gas with the power of a trillion suns. Conditions are still more extreme in the black hole's interior, within the surface of no return known as the event horizon, where the very fabric of space and time may be ripped apart. All this is happening in a relentlessly expanding universe that began about fourteen billion years ago with an all-encompassing explosion, the Big Bang, that makes all the other phenomena I have described seem mild and inconsequential by comparison. And that whole universe is just a sliver of an enormously larger entity, the multiverse, which includes vast numbers of such universes. The physical world is not only much bigger and more violent than it once seemed, it is also immensely richer in detail, diversity, and incident, yet it all proceeds according to elegant laws of physics that we understand in some depth. I do not know which is more awesome, the phenomena themselves or the fact that we know so much about them. How do we know? One of the most remarkable things about science is the contrast between the enormous reach and power of our best theories and the precarious local means of production.